On a Thursday evening three weeks ago, three men and a teenage boy from a boarding school in Bogor, West Java, got off a budget airline at Changi Airport.

They were dressed in T-shirts, jeans and casual jackets, and carried backpacks – not unlike many young Indonesian travellers.

But something about the group seemed odd to the undercover officer monitoring the passengers coming through the arrival gate at 9pm on Feb 18. His hunch proved right when they took the escalators a floor down to the immigration counters.

… “Singapore was not a launch pad for their travel – they came here just to get their passports stamped,” said Professor Rohan Gunaratna, who heads the International Centre for Political Violence and Terrorism Research at Nanyang Technological University’s S. Rajaratnam School of International Studies. “They have also admitted to the authorities in Indonesia that their intention was to travel to Syria and be part of ISIS.”